The device SR04 is a differential controller, designed for control of solar systems with one or two collectors, boiler, storage vessel and a pool. SR04 also is applicable in smaller installations, including some of those elements. SR04 can heat the boiler from different sources – solar panel, electrical heater, boiler. Heating with energy from electrical grid can be programmed in fixed time zones. There is function against locking of the pumps, manual on/off switching the outputs, trial period, actuality of the measurements, non-volatile clock.